Process for the preparation of metal sulfamates



United States Patent Delaware No Drawing. Filed Aug. 14, 1963, Ser. No. 301,984 14 Claims. (Cl. 23-414) This invention relates to a process for the preparation of metal salts of sulfamic acid.

It is well known that metal'sulfamates are useful as electrolytes for the electrodeposition of nickel and other metals. As contrasted with electroplating baths that contain such other electrolytes as cyanides, chlorides, silicofiuorides, or sulfates, baths containing metal sulfamates are easier to operate and to control and are usually less toxic and less corrosive. Electrodeposits of the metals from the sulfamate plating baths are characterized by low internal stress, excellent grain structure and ductility, and other valuable properties.

Heretofore the metal sulfamates that are used in electroplating baths have generally been prepared by a series of reactions in which a metal carbonate, obtained by adding sodium carbonate to a solution of the metal sulfate or chloride, is reacted with sulfamic acid to form the desired salt. In the commercial practice of this process, the metal salts are often contaminated with by-product salts of the reactions, such as sodium sulfate or sodium chloride. In addition, elevated reaction temperatures are necessary for the completion of the reaction of the metal carbonate and sulfamic acid and for the complete elimination of carbon dioxide. Under the conditions required for this reaction, that is, elevated temperature and low pH, sulfamic acid is readily hydrolyzed to ammonium acid sulfate. This reaction may be represented as follows:

The ammonium ion that results from this hydrolysis reaction.isa harmful impurity in the metal sulfamate since, for example, it will cause embrittlement of nickel electrodeposits from nickel sulfamate plating baths. In addition this process involves the use as an intermediate of metal chlorides or sulfates which are usually a relatively costly source of the metals.

Another process that has been suggested for the preparation of metal sulfamates involves the direct reaction of a metal with sulfamic acid in aqueous solution. When this reaction is carried out at high temperatures, however, the sulfamic acid is hydrolyzed to an appreciable extent thus forming metal and ammonium sulfates. When lower temperatures are employed, the reaction between the metal and the acid takes place so slowly and the yield of the metal salt is so low that the process is commercially impractical.

It is thereforean object of this invention to provide a simple, efficient, and economical process for the production of metal sulfamates. It is a further object to provide a process for the production of metal sulfamates that are substantially free from metal and ammonium sulfates and other contaminants. Other objects will be apparent from the detailed description of the invention that follows.

These objects are accomplished in accordance with the present invention by contacting a finely-divided metal with sulfamic acid in the presence of water and oxygen. The resulting metal sulfamates, which contain only very small amounts of ammonium salts and other contaminants, are obtained in a substantially quantitative yield.

A wide variety of metals can be converted to their sulfamate salts by means of the process of this invention. This process is of particular value in the preparation of sulfamate salts of nickel, cobalt, iron, lead, copper,

cadmium, zinc, aluminum, and mixtures of these metals. The metal is generally used in the form of a powder so that a large metal surface is exposed to the reaction and the conversion of the metal to its salt is accomplished readily and completely.

Equivalent amounts of metal and sulfamic acid or a stoichiometric excess of either the metal or the acid may be used in this process. It is generally preferred to use a 5% to molar excess of the metal.

The conversion of the metal to metal sulfamate may be conveniently accomplished by introducing oxygen or an oxygen-containing gas into a suspension of the finelydivided metal in an aqueous solution of sulfamic acid. The addition of the oxygen is continued until substantially no unreacted metal remains in the reaction mixture or until the pH of the reaction mixture has reached a value in the range of approximately 4.0-6.5. When the metal sulfamate solution is to be used in an electroplating bath that is operated at a pH in the range of 1.0-6.5, the acidity of the sulfamate solution may be brought to the required level by the addition of sulfamic acid.

The metal sulfamates may if desired be recovered from the aqueous solutions prepared in accordance with this invention by procedures that are well known in the art, for example, by evaporation of the solution to dryness. It is generally preferred, however, that these solutions or solutions that have been concentrated under atmospheric pressure or sub-atmospheric pressure be used in electroplating baths in order to minimize the hydrolysis of any sulfamic acid that may be present and consequently to minimize the contamination of the bath with ammonium 10118.

The present process for the production of metal sulfamates may be carried out under atmospheric pressure, or superatmospheric pressures. Although the solubility of oxygen in water and the reaction rate are increased at superatmospheric pressures, it is generally more economical and more convenient to prepare the metal sulfamate at atmospheric pressure. At atmospheric pressure, the reaction is ordinarily carried out at a temperature in the range of approximately 15 C. to 65 C. Reaction temperatures above 65 C. are not usually employed, since at such temperatures sulfamic acid is readily hydrolyzed. It is generally preferred to carry out the reaction at a temperature in the range of 35 C. to 50 C.

The amount of water that is used as the reaction medium is not critical provided that it i sufiicient to dissolve the metal sulfamate that is formed. It is "generally prefeared that an amount of water be used that will dissolve at least 25% and preferably all of the sulfamic acid that is used in the reaction at the temperature at which the reaction is carried out. When the amount of water used is less than that required to dissolve all of the metal sulfamate and/or the sulfamic acid, the reaction may take place slowly or fail to reach completion as the result of the formation of a layer of solid acid or sulfamate on some of the particles of unreacted metal. This inhibiting effect may be avoided when the amount of water usedis less than that required to dissolve all of the acid by adding the acid in several portions to a suspension of the finely-divided metal in water and allowing each portion of the acid to react to form the more soluble metal sulfamate before the next portion is added. Larger amounts of water than are required to dissolve the sulfamic acid may be present, but there is no particular advantage to their use. Excellent results have been obtained when approximately 2 parts to 25 parts by weight of water was used per part by weight of sulfamic acid.

For the conversion of the metal to the sulfamate salt to take place efiiciently, it is necessary that oxygen be present in the reaction mixture. The oxygen may be added as such or as a compound, for example, a peroxide,

that will decompose under the reaction conditions to release oxygen. The addition of oxygen is ordinarily accomplished by bubbling air at atmospheric pressure through the mixture during the reaction. The amount of oxygen that is added to the reaction mixture can be varied within wide limits. In most cases air is bubbled through the reaction mixture at such a rate that a total of approximately 2 moles to 100 moles and preferably 5 moles to 30 moles of oxygen is provided per mole of the metgl. Larger amounts of oxygen may be added if desire Thi invention is further illustrated by the examples that follow. It is to be understood that these examples are given solely for the purpose of illustration and that the invention is not to be regarded as being limited to any of the specific materials or conditions recited therein except as set [forth in the appended claims.

Example I A mixture of 49 grams of 99% sulfamic acid, 400 ml. of water, and 117.4 grams of powdered nickel (particle size: 95% through a #200 U.S. Standard Sieve) was agitated and heated to 40 C. Air wa blown into the mixture at the rate of 140 liters per hour while the mixture was agitated and maintained at 40 C.45 C. When the pH of the mixture had risen to 5.0, a second portion of 49 grams of sulfamic acid was added. Air injection was continued at the rate of 140 liters per hour, and the mixture was heated at 40 C.-45 C. until the pH had again risen to 5.0. This procedure was repeated until 196 grams of acid had been added. A total of 12 hours was required for the addition of the acid. After all of the acid had lbl1 added, the mixture was filtered to remove unreacted nickel. The filtrate was concentrated by boiling it in an open vessel and then cooled to 25 C. The pH of the nickel sulfamate solution Was brought to 4.35 by the addition of a small amount of sulfamic acid. There was obtained 557 grams of a dark green solution that contained 10.5% of nickel which indicated that 99.6% of the sulfamic acid had been converted to nickel sulfamate. The product, which had a specific gravity of 1.48, contained 0.07% of sulfate, which indicated that substantially no hydrolysis of the sulfamic acid had occurred.

Example ll A'mixture of 196 grams of 99% sulfamic acid, 1800 ml. of water, and 62 grams of powdered cobalt (95% cobalt content; particle size: 100% through a #100 U.S. Standard Sieve, 5% through a. #200 U.S. Standard Sieve) was agitated and heated to 50 C. Air was blown into the mixture at the rate of 60 liters per hour for 6 hours while the mixture was agitated and maintained at 50 C.- 55" C. At the end of this period, the pH of the reaction mixture was 6.2. After filtration there was obtained 1963 grams of a reddish-purple solution that contained 3% of cobalt, which indicated that all of the cobalt had been converted to cobalt sulfamate. This solution was concentrated by heating it at its boiling point in an open vessel and then cooled to 25 C. The pH of the solution was brought to 3.95 by the addition of a small amount of sulfamic acid. There was obtained 530 grams of a cobalt sulfamate solution that contained 11.1% of cobalt and less than 0.005% of sulfate. Its specific gravity was 1.48.

Example III A mixture of 294 grams of 99% sulfamic acid, 2800 ml. of water, and 55.8 grams of powdered iron (particle size: 100% through a #100 U.S. Standard Sieve) was agitated and heated to 55 C. Air was blown into the mixture at the rate of 90 liters per hour for 5 hours during which time the mixture was agitated and maintained at 55 -60 C. At the end of this period, the pH of the mixture was 1.4. After filtration there was obtained 3040 grams of a pale green iron sulfamate solution that contained 1.8% of iron, which indicated that 98% of the iron had been converted to iron sulfamate. This solution was concentrated under reduced pressure and then cooled to 25 C. There was obtained 507 grams of an iron sulfamate solution that contained 10.8% of iron and 0.03% of sulfate.

Example IV A mixture of 196 grams of 99% sulfamic acid, 3700 ml. of water, and 112.4 grams of powdered cadmium (particle size: 100% through a #100 U.S. Standard Sieve) was agitated and heated to 40 C. Air was blown into the mixture at the rate of lite-rs per hour for 12 hours while the mixture was agitated and maintained at 40-45 C. At the end of this period, the pH of the mixture was 2.1. After filtration, there was obtained 3915 grams of a water-White cadmium sulfamate solution that contained 2.8% of cadmium and 0.01% of sulfate. The conversion of cadmium to cadmium sulfamate was 97.6%.

Example V A mixture of 196 grams of 99% sulfamic acid, 1600 ml. of water, and 66.7 grams of powdered copper (particle size: 95% through a #200 U.S. Standard Sieve) was agitated and heated to 45 C. Air was blown into the mixture at the rate of liters per hour for 4 hours while the mixture was agitated and maintained at 45 50 C. At the end of this period, the pH of the reaction mixture was 4.2. After filtration, there was obtained 1760 grams of a deep blue copper sulfamate solution that contained 3.6% of copper, which indicated that 99.7% of the copper had been converted to copper sulfamate. This copper sulfamate solution was concentrated by heating it at its boiling point and then cooled to 25 C. There was obtained 320 grams of a copper sulfamate solution that contained 12% of copper and 0.09% of sulfate.

Example VI A mixture of 196 grams of 99% sulfamic acid, 1600 ml. of Water, and 228 grams of powdered lead (particle size: 95% through a #100 U.S. Standard Sieve) was agitated and heated to 35 C. Air was blown into the mixture at the rate of 140 liters per hour for 14 hours while the mixture was agitated and maintained at 35 40 C. At the end of this period, the pH of the mixture was 3.3. After filtration, there was obtained 1870 grams of a water-white lead sulfamate solution that contained 10.2% of lead.

Example VII A mixture of 294 grams of 99% sulfamic acid, 2700 ml. of water, and 27 grams of very finely divided aluminum dust was agitated and heated to 40. Air was blown into the mixture at the rate of 140 liters per hour for 17 hours during which time the mixture was agitated and maintained at 4 045 C. After filtration there was obtained 2990 grams of a slightly 'hazy solution that contained 0.80% of aluminum and 0.005% of sulfate. The pH of the solution was 1.4.

I claim:

1. The process for the production of metal sulfamates which comprises introducing ,a gas selected from the group consisting of oxygen and an oxygen-containing gas into a suspension of a finely-divided metal selected from the group consisting of nickel, cobalt, iron, lead, copper, cadmium, zinc, aluminum, and mixtures thereof in an aqueous solution of sulfamic acid, said suspension containing an amount of the metal that is at least equivalent to the amount of sulfamic acid that is present and containing an amount of water sufiicient to dissolve the metal sulfamate that is formed at a temperature in the range of approximately 15 C. to 65 C., thereby forming an aqueous solution of said metal sulfamate.

The Process of claim 1 wherein the oxygen-containing gas is air.

3. The process of claim 1 wherein the reaction temperature is in the range of 35 C. to 50 C.

4. The process of claim 1 wherein the metal is nickel.

5. The process of claim 1 wherein the metal is cobalt.

6. The process of claim 1 wherein the metal is iron.

7. The process of claim 1 wherein the metal is cadmium.

8. The process of claim 1 wherein the metal is copper.

9. The process for the production of nickel sulfamate which comprises introducing air into a suspension of finely-divided nickel in an aqueous solution of sulfamic acid, said suspension containing a 5% to 100% stoichiometric excess of nickel and containing an amount of water sufiicient to dissolve the nickel sulfamate that is formed, at a temperature in the range of approximately 15 C. to 65 C. until substantially all of the sulfamic acid has been converted to nickel sulfamate thereby forming an aqueous solution of nickel sulfamate.

10. The process of claim 9 wherein the total amount of air introduced is that which will provide approximately 2 moles to 100 moles of oxygen for each mole of metal in the suspension.

11. The process for the production of nickel sulfamate which comprises introducing air into a suspension of finely-divided nickel in an aqueous solution of sulfamic acid, said suspension containing a 5% to 100% stoichiometric excess of nickel and containing an amount of water sufiicient to dissolve the nickel sulfamate that is formed, ,at a temperature in the range of 35 C. to 50 C. until substantially all of the sulfamic acid has been converted to nickel sulfamate and filtering the resulting suspension thereby obtaining an aqueous solution of nickel sulfamate having a pH in the range of approximately 4.0 to 6.5.

12. The process of claim 11 wherein the total amount of air introduced is that which will provide approximately 5 moles to 30 moles of oxygen for each mole of metal in the suspension.

13. The process for the production of metal sulfamates which comprises introducing oxygen into a mixture containing (a) a finely-divided metal selected from the group consisting of nickel, cobalt, iron, lead, copper, cadmium, zinc, aluminum, and mixtures thereof, (b) sulfamic acid, and (c) Water, said mixture being maintained at a temperature in the range of approximately 15 C. to 65 C. during the introduction of the oxygen and containing an amount of water that is suflicient to dissolve the metal sulfamate that is formed.

14. The process of claim 13 wherein the reaction mixture is maintained at a temperature in the range of C. to C. during the addition of the oxygen.

References Cited by the Examiner UNITED STATES PATENTS 2,765,213 10/1956 Beekman 231 14 OSCAR R. VERTIZ, Primary Examiner.

EARL C. THOMAS, Examiner. 

1. THE PROCESS FOR THE PRODUCTION OF METAL SULFAMATES WHICH COMPRISES INTRODUCING A GAS SELECTED FROM THE GROUP CONSISTING OF OXYGEN AND AN OXYGEN-CONTAINING GAS INTO A SUSPENSION OF A FINELY-DIVIDED METAL SELECTED FROM THE GROUP CONSISTING OF NICKEL, COBALT, IRON, LEAD, COPPER, CADMIUM, ZINC, ALUMINU, AND MIXTURES THEREOF IN AN AQUEOUS SOLUTION OF SULFAMIC ACID, SAID SUSPENSION CONTAINING AN AMOUNT OF THE METAL THAT IS AT LEAST EQUIVALENT TO THE AMOUNT OF SULFAMIC ACID THAT IS PRESENT AND CONTAINING AN AMOUNT OF WATER SUFFICIENT TO DISSOLVE THE METAL SULFAMATE THAT IS FORMED AT A TEMPERATURE IN THE RANGE OF APPROXIMATELY 15*C. TO 65*C., THEREBY FORMING AN AQUEOUS SOLUTION OF SAID METAL SULFAMATE. 